Digital detector of an analog signal

ABSTRACT

A circuit combination of integrated circuit (IC) digital devices for detecting an analog signal of a selected frequency and amplitude is disclosed. The circuit combination is a specialpurpose digital filter of a predetermined bandwidth determined by the sample time TS duration and the low FL and high FH frequencies of the passable analog signal frequency having a carrier frequency FA. The analog signal is initially tested for minimal amplitude and converted to a digital signal by a conventional comparator circuit. The pulses of the digital signal are counted over the sample time TS and compared to the passable bandwidth: if the analog signal frequency FA (FL &lt; OR = FA &lt; OR = FH) is within the bandpass, i.e., passable, a first binary signal is produced; alternatively, if the analog signal frequency FA (FL&gt;FA&gt;FH) is without the bandpass, i.e., not passable, a second binary signal is produced. Sample times continue throughout the detection-comparing operation to ensure a continuous filtering process.

United States Patent 091 Cardon et al.

[ Oct. 29, 1974 DIGITAL DETECTOR OF AN ANALOG Primary Examiner-Stanley D. Miller, Jr.

SIGNAL Attorney Agem, or Firm-Kenneth T. Grace; Thomas [75] Inventors: Carlos D. Cardon; Lawrence P. Nlkolal; John Domy Griffone, both of Salt Lake City, Utah [57] ABSTRACT Assigneei P Rand Cfl p New A circuit combination of integrated circuit IC) digital York, devices for detecting an analog signal of a selected fre- [22] Filed: Aug 30, 1973 quency and amplitude is disclosed. The circuit combination IS a special-purpose digital filter of a predeter- PP 393,117 mined bandwidth determined by the sample time T duration and the low F and high F frequencies of the [52 us. Cl 328/138, 307/233, 307/295, passable anabg Sign l f y f 3 came i 328mm 328/167 quency F The analog signal 18 lnltially tested for mm- [5 I] In Cl H "03d 3/00, "03b 3/04, H03k 5/20 lmal amplitude and converted to a digital signal by a [58] Field of Search 307/233, 295; 328/138, 9"." comparao' The Pulses the 328/140 32 4 /78 D digital signal are counted over the sample time T and compared to the passable bandwidth: if the analog sig- [561 Reierences Cited gz s ii p ais bie a firSt binag s i gr i zil i s gi dii c ei UNITED STATES PATENTS alternatively, if the analog signal frequency F 3.537 O0l ill/I970 Friend 328/[38 (FL FA FH) is without the bandpass Le not pass- 3'543l72 l [970 SePPFler 307/233 able, a second binary signal is produced. Sample times continue throughoutthe detection-comparing opera- 3:761:80) 9/l973 Lockitt et aiifi I: 328/140 to ensure a cmmuous filtermg pmcess' 3,769,583 10/1973 Spencer et al7 328/140 3 Claims 4 Drawing Figures I0 C L L. I o {IO-21' I 20I I [30'I I A LMTER 5 EDGE c BINARY |-UAMPLIFIER Q Z I DETECTOR I COUNTER l 1 I J I r BAI JE ESGE eAh b E eE I DETECTOR F DECODER DETECTOR L40 I i ,'4 Tz 74o -F D I svNcwRomzEn TIME 7 EDGE GENERATOR I I DETECTOR smcnnowzsn I l 1 H 80 so 70' L L l -1 60-2 1 F j I TIME E TIME BASE I F I TIME BASE I 0 BASE EDGE DETECTOR EM DETECTOR I GENERATOR (LEADING EDGE) I (TRAILING EDGE) l l l 1 DIGITAL DETECTOR OF AN ANALOG SIGNAL BACKGROUND OF THE INVENTION Prior art detectors of an analog signal of a selected frequency and amplitude have been designed using an analog filter that passes only an analog signal of the selected frequency and amplitude followed by a full-wave or half-wave rectifier and then a Schmitt trigger. Because of the availability of inexpensive and reliable digital circuits it is desirable that previous analog techniques be replaced by digital techniques as proposed by the present invention.

SUMMARY OF THE INVENTION In the digital filter of the present invention an analog input signal ofa frequency F is initially tested for minimum amplitude and then converted to a binary digital waveform which is edge detected to provide an output pulse for every cycle of the analog input signal. The first output pulse sets a sample time generator and the pulses are counted over the sample time T If the pulse count is within the bandpass at any time during the sample time T 'the counter and a binary decoder set a flip-llop to a True state. This flip-flop is sampled at the end of the sample time and the True output is transferred to a storage element which is switched to the True condition. The True condition of the storage element after a one pulse width delay time then resets the counter back to 0. A time generator synchronizer driven by the output of the edge detector is disabled if the condition of the storage element is True. During the next successive sample time T the procedure is repeated with the counter counting the number of pulses from the edge detector. If the number of pulses counted is within the bandpass the binary decoder continues coupling a True condition to the storage element with the counter reset as before and the time generator synchronizer being disabled. If during the next sample time T the counter counts a number of pulses without the bandpass the binary decoder couples a False output signal indicating that the analog input signal is ofa frequency outside the bandpass. This False condition signal is delayed one pulse width to activate the time generator synchronizer in preparation for the next incoming pulse from the edge detector which incoming pulse intiates the sample time generator after which the detector-comparing operation is repeated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a block diagram of the special-purpose digital filter of the present invention.

FIG. 2, consisting of FIGS. 20, 2b. is a logic level drawing of the special-purpose digital filter of FIG. 1.

FIG. 3 is a timing diagram illustrating the operation of the special-purpose digital filter of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT With particular reference to FIG. I there is presented a block diagram of the special-purpose digital filter of the present invention. the elements thereof being illustrated in detail at their logic level in FIGS. and 2b. The special-purpose digital filter of the present invention basically establishes a fixed sample time T during which the actual number N of cycles or pulses of a sampled signal are counted. The number N is then compared to the minimum number N, and the maximum number N, of cycles or pulses that define the bandpass width of the filter. If within that range, i.e., N,

N :5 N a first True signal is generated and if without the range, i.e.. N, N, N a second False signal is generated. The True and/or False signals are then set into a flip-flop and the flip-flop output is in turn clocked into the output storage element (flip-flop) at the end of the sample period. Thus the True condition of the output storage element indicates that a signal meeting the amplitude and frequency conditions is present at the input to the circuit. Conversely. the False condition indicates that the signal does not meet these conditions. Using the timing diagram of FIG. 3 to explain the operation of the present invention illustrated in FIGS. I, 2a. 2b certain parameters shall be assumed by way of example to better illustrate the operation of the present invention in its preferred embodiments of FIGS. 20, 2b:

FL 7: HZ

F H 3,000 Hz Thus the sampled signal shall be sampled over a duration of 6.67 X l0 sec. and if the sampled signal frequency F is within the bandpass width, i.e., N, N, N the filter shall generated a True signal output and, alternatively. if the sample signal frequency is without the bandpass width the filter shall generate a False signal output.

Referring to the signal waveforms of FIG. 3, the analog signal A of a frequency F is coupled to comparator l0. Signal A is initially coupled to amplifier l0-I which is an isolation and threshold detector which compares signal A to a threshold level and if signal A is above the threshold level couples signal A to converter [0-2. Converter 10-2 converts the analog signal A of a frequency F to the digital signal B. The digital signal B is then coupled to edge detector 20 which produces, as an output. signal C which consists of a single short duration output pulse for every complete input cycle of signal B. Signal C is, in turn, coupled in parallel to counter 30 and sample time controller 40. At binary counter 30-I the pulses of signal C, beginning at time t are counted with the running total count being decoded by binary decoder 30-2 which, in turn couples a decoder True signal to lower band edge detector 303 if the decoded binary count is equ-al to the lower bandpass and a decoder False signal to upper band edge detector 30-4 if the decoded binary count is above the upper bandpass. At sample time controller 40 the first pulse of signal C triggers time generator synchronizer 40-l coupling a single short duration pulse to synchronizer edge detector 40-2 that couples the signal D to the sample time generator 60. Signal D triggers time base generator 60-1 to generate signal E which is, in turn. coupled to time base leading edge detector 602 which generates as an output therefrom signal F which is coupled to edge triggered bistable multivibrator or flip-flop 80-] of memory element 80 by way of inverter 80-2 and to time base trailing edge detector which generates an output signal G. Signal G resets the binary counter 30-1 to O and through NAND gate 70-3 and inverter 70-4 sets bistable multivibrator or flip-flop 70-2. At this time. edge triggered bistable multivibrator -1 of memory element 80 is coupling a relatively low level False state of output signal 0 to an output line 80-3 and as a first input to NAND gate 50-] of synchronizer controller 50.

Counter 30 is set to a bandpass ofa count of 6 20, and. accordingly, at the count of 6 binary decoder 30-2 couples a True decode pulse to lower band edge detector 30-3 which. in turn couples decode True signal H to bistable multivibrator 70-2 causing it to change its state. Binary counter 30-l continues counting the subsequent pulses 7 19 of signal C causing lower band edge detector 30-2 to remain in its previously set True State.

At the end of the sample time T time base generator 60-l couples the second pulse of signal E to time base leading edge detector 60-2 which. in turn. couples the second pulse of signal F to edge triggered bistable multivibrator 80-1 by way of inverter 80-2 which gates the state of bistable multivibrator 80-2 therein causing memory element 80 to couple to its output line the relatively high level True state of output signal and through NAND gate 70-3 and inverter 70-4 causes bistable multivibrator 70-2 to change to a False state. The concurrent application of the signal G and signal 0 at NAND gate 50-] disables the time generator synchronizer 40-l.

Under the above described conditions the input signal A has been assumed to be within the bandpass of a pulse count of 6 20, e.g.. F,,= 900 Hz. F 3.000 H2 at a sample time T of 6.67 x l0" see. If the count had been greater than 20 at time t., e.g.. after sample time T binary decoder -2 would have coupled the appropriate signal to upper band edge detector 30-4 which. in turn. would have coupled a decode False pulse to NAND gate 70-3 and inverter 70-4 which. in turn. would have changed the state of bistable multivibrator 70-2 which False state of bistable multivibrator 70-2 would have caused edge triggered bistable multivibrator 80-l to couple the low level False state of output signal 0 to output line 80-3 when gated by inverter 80-2. Alternatively. if the count had been less than 6 at time r.. e.g.. after sample time T binary decoder 30-2 would not have coupled any True decode signal to lower band edge detector 30-3 whereby no high level pulse of signal H would have been coupled to bistable multivibrator 70-2 causing edge triggered bistable multivibrator 80-l to continue coupling the relatively low level False state of output signal 0 to output line 80-3 of memory 80 when triggered by inverter 80-2. With the output signal A continuing to be of a frequency F within the bandpass. memory element A continues coupling its relatively high level True state ofoutput signal 0 to its output line 80-3. However. as at the end of the sample time T at time t. the second pulse of signal F from time base trailing edge detector 70-l has reset binary counter 30-l to O the above described sequence repeats itself testing the incoming signal A for its frequency F to determine. if at any time, it is within or without the bandpass and to provide a corresponding high level True state or low level False state of output signal 0 on its output line 80-3.

What is claimed is:

l. A digital detector of an analog signal. comprising:

means receiving an input analog signal ofa frequency F v for generating a digital signal ofa frequency F therefrom;

counting means coupled to said digital signal for counting the number of pulses N thereof during a preset sample time T and generating a decode True signal if the counted number of pulses is equal to or greater than a preset low N, number of pulses and generating a decode False signal if the counted number of pulses is greater than a preset high N number of pulses for defining a preset bandwith N,

NA u;

an output flip-flop for generating as the alternative output signals an output True signal or an output False signal indicating that said counting means has counted a number of pulses N, of said digital signal that is within or without. respectively, said preset bandwidth;

a decoder flip-flop responsively coupled to said decode True signal and said decode False signal for storing a decoder True signal or a decoder False signal;

means gating the decoder True signal or the decoder False signal from said decoder flip-flop into said output flip-flop for storing and generating an output False signal or an output True signal, respectively. on a detector output line therefrom.

2. A digital detector of an analog signal, comprising:

means receiving an input analog signal of a frequency F, for generating a digital signal comprising a series of short duration pulses of a frequency F one pulse for every cycle of said input analog signal;

sample time base generator means coupled to said digital signal for generating. when effected by a first pulse of said digital signal, a sample time signal comprising a first sample time pulse and after the sample time T a second sample time pulse;

counting means coupled to said digital signal for counting the number of pulses N thereof during said sample time T and generating a decode True signal if the counted number of pulses is equal to a preset low M count and generating a decode False signal if the counted number of pulses is greater than a preset high N count for defining a preset bandwidth N s N. s N

means coupling said sample time signal to said counting means for resetting said counting means to a zero count upon receipt of said first sample time pulse;

output memory means for generating as the alternative output signals an output True signal or an output False signal indicating that said counting means has counted a number of pulses of said digital signal that is within or without. respectively. said preset bandwidth;

decoder memory means coupled to said decode True signal and said decode False signal for coupling a decoder True signal or a decoder False signal to said output memory means;

means coupling said second sample time pulse to said output memory means for gating the decoder True signal or the decoder False signal from said decoder memory means into said output memory means and coupling an output True signal or an output False signal. respectively. therefrom on a detector output line.

3. The digital detector of claim 2 further including:

output False signal.

IN THE PREIELPATENT:

Data element 57 1, ABSTRACT, Front Page, Line 13,

"FA(FL FA PH) should be FA(FL FA FH) Signed and sealed this 31st day of December 1974.

SEAL) Attest:

IIcCOY M. GIBSON JR. (5. ZEARSHALL DANN Attesting Officer Commissiqner of Patents 

1. A digital detector of an analog signal, comprising: means receiving an input analog signal of a frequency FA for generating a digital signal of a frequency FA therefrom; counting means coupled to said digital signal for counting the number of pulses NA thereof during a preset sample time TS and generating a decode True signal if the counted number of pulses is equal to or greater than a preset low NL number of pulses and generating a decode False signal if the counted number of pulses is greater than a preset high NH number of pulses for defining a preset bandwith NL < OR = NA < OR = NH; an output flip-flop for generating as the alternative output signals an output True signal or an output False signal indicating that said counting means has counted a number of pulses NA of said digital signal that is within or without, respectively, said preset bandwidth; a decoder flip-flop responsively coupled to said decode True signal and said decode False signal for storing a decoder True signal or a decoder False signal; means gating the decoder True signal or the decoder False signal from said decoder flip-flop into said output flip-flop for storing and generating an output False signal or an output True signal, respectively, on a detector output line therefrom.
 2. A digital detector of an analog signal, comprising: means receiving an input analog signal of a frequency FA for generating a digital signal comprising a series of short duration pulses of a frequency FA, one pulse for every cycle of said input analog signal; sample time base generator means coupled to said digital signal for generating, when effected by a first pulse of said digital signal, a sample time signal comprising a first sample time pulse and after the sample time TS a second sample time pulse; counting means coupled to said digital signal for counting the number of pulses NA thereof during said sample time TS and generating a decode True signal if the counted number of pulses is equal to a preset low NL count and generating a decode False signal if the counted number of pulses is greater than a preset high NH count for defining a preset bandwidth NL < or = NA < or = NH; means coupling said sample time signal to said counting means for resetting said counting means to a zero count upon receipt of said first sample time pulse; output memory means for generating as the alternative output signals an output True signal or an output False signal indicating that said counting means has counted a number of pulses of said digital signal that is within or without, respectively, said preset bandwidth; decoder memory means coupled to said decode True signal and said decode False signal for coupling a decoder True signal or a decoder False signal to said output memory means; means coupling said second sample time pulse to said output memory means for gating the decoder True signal or the decoder False signal from said decoder memory means into said output memory means and coupling an output True signal or an output False signal, respectively, therefrom on a detector output line.
 3. The digital detector of claim 2 further including: gating means coupled to said detector output line and said sample time base generator means for generating a new sample time signal when affected by an output False signal. 